1. Field of the Invention
The present invention relates to a beam forming method capable of reducing a transmission frequency of a training sequence and a multiple antenna system using the same.
2. Description of the Related Art
Recently, schemes to solve a lack of telecommunications frequency resources have been sought. One of these schemes, millimeter wave band communication, is drawing great attention due to the merits of using broadband to obtain a high transmission rate. In addition, since the miniaturization and lightness of an RF device may be implemented due to a short wavelength, international standardization standards for wireless local area networks (WLAN) and a wireless personal area networks (WPAN) have been developed.
In millimeter wave band communication, a beam forming technique using multiple antennas has been widely adopted; in particular, in the millimeter wave band communication, a MIMO-OFDM system in which orthogonal frequency-division multiplexing (OFDM) is coupled with a multi input multi output (MIMO) scheme has been used due to a high spatial correlation of a millimeter wave band channel. As the beam forming technology used in the MIMO-OFDM system, there is provided a codebook-based symbol beam forming technology. In this case, beam forming, one of a plurality of schemes used for a smart antenna, is a technology in which a beam is only irradiated from an antenna to a specific corresponding terminal. The smart antenna may be implemented using a plurality of antennas in order to increase the efficiency thereof. A smart antenna scheme in which a plurality of antennas are mounted in both a transmitter and a receiver is referred to as multi input multi output (MIMO).
The codebook-based symbol beam forming technology is a technology in which a transmitting and receiving weight vector, capable of optimizing a cost function, is selected through a transmission of a training sequence without estimating channel information. That is, it is essential in a transmission procedure of the training sequence for selecting the transmitting and receiving weight vector prior to transmitting data. However, in performing the transmission procedure of the training sequence, the transmission frequency of the training sequence is increased and thus, an excessive amount of time is consumed.